In jet engines a seal is conventionally provided on the engine casing walls adjacent the ends of the rotor blades and on the ends of the stator blades adjacent the rotor. The function of the seals is to prevent leakage around blade tips with a resultant drop in air pressure. The sealant material must be abradable so as to prevent damage to the blades in the event blade tips strike the material during an engine unbalance condition.
A typical seal used in jet engines comprises an epoxy resin and phenolic microspheres. When contacted with rotating blade tips, this material abrades into a fine particle dust. In the fan section of a jet engine, most of this dust passes out of the engine through the by-pass duct. However, during an engine unbalance condition, in the booster stages, the abraded seal material flows into the higher temperature, higher pressure area of the engine. The conditions in this area are sufficient to cause essentially instantaneous decomposition of the material, resulting in an uncontrolled pressure rise with a possible following explosion within the engine.
It is a principle object of this invention, therefore, to provide a non-combustible, abradable sealant composition for jet engines.
Another object of the invention is to provide a seal material which will withstand service temperatures as high as 2500.degree. F.
Other objects and advantages of the invention will become apparent to those skilled in the art upon consideration of the accompanying disclosure.